Spectrophotometer and spectrophotometry method

ABSTRACT

The present invention responds flexibly to and corrects concentration changes that are caused by changes between the temperature when a correction calibration curve is created and the temperature when a test sample is measured, without having to correct the calibration curve. More specifically, a spectrophotometer measures concentrations of measurement target components contained in a test sample from an optical spectrum obtained by irradiating light onto the test sample, and includes a concentration calculation unit that calculates concentrations of the measurement target components from the optical spectrum using a calibration curve, and a concentration correction unit that, using a temperature correction formula corresponding to a wavelength region or a wavenumber region in which concentrations of the measurement target components are being determined, corrects concentration changes in the measurement target components that accompany temperature differences between a temperature when the calibration curve is created and a temperature when the concentrations are measured.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Application No.2017-166784, filed Aug. 31, 2017, the disclosure of which isincorporated in its entirety by reference herein.

TECHNICAL FIELD

The present invention relates to a spectrophotometer that employsinfrared spectroscopy such as, for example, Fourier-transform infraredspectroscopy, and to a spectrophotometry method.

TECHNICAL BACKGROUND

Conventionally, as is shown in Patent Document 1, an FTIR(Fourier-transform infrared spectroscopy) method is used in order tomeasure concentrations of measurement target components contained in atest sample such as, for example, exhaust gas or the like.

A spectrophotometer that uses this FTIR method is provided with ameasurement cell into which a test sample is introduced, a lightirradiation unit that irradiates infrared light onto the measurementcell, and a photodetector that detects an intensity of light transmittedthrough the measurement cell. This spectrophotometer calculates anoptical absorption spectrum of exhaust gas using light intensity signalsobtained by the photodetector, and calculates the concentration of themeasurement target component from the absorbance of this opticalabsorption spectrum. Here, when calculating a concentration from theabsorbance of the optical absorption spectrum, a calibration curvecomparing the absorbance of the optical absorption spectrum with theconcentration of the measurement target component shown by thisabsorbance is used.

In the above-described spectrophotometer, during the measurement of atest sample, the temperature of the measurement cell is adjusted so thatit remains constant. If the temperature of the measurement cell differsfrom the temperature of the measurement cell at the time when thecalibration curve was created, then discrepancies occur in theconcentrations obtained from the calibration curve.

As is shown in Patent Document 2, a spectrophotometer that corrects thecalibration curve at each temperature has been developed in order toreduce discrepancies caused by these temperature changes. Morespecifically, using the same sample, this spectrophotometer measures aspectrum in advance at a reference temperature and at a differenttemperature from the reference temperature, and thereby determines adifference spectrum thereof. By then modifying the difference spectrumthat has been multiplied by a coefficient in accordance with thetemperature changes in the sample such that it is set to the measurementspectrum, the difference spectrum is converted into an equivalentspectrum to the spectrum measured at the reference temperature. Thespectrophotometer then corrects the calibration curve calculationresults obtained from temperature changes in the sample.

DOCUMENTS OF THE PRIOR ART Patent Documents

[Patent document 1] Japanese Unexamined Patent Application (JP-A) No.H9-101257

[Patent document 2] Japanese Unexamined Patent Application (JP-A) No.2005-331386

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention was therefore conceived in order tocomprehensively solve the above-described problems, and was conceivednot with the idea of correcting the calibration curve, but with the ideaof correcting concentrations obtained from the calibration curve usingtemperature.

Here, using an equation of state for a gas, because the concentrationsof measurement target components decrease as the absolute temperaturethereof increases, correcting measurement discrepancies inconcentrations obtained from a calibration curve using a correctionformula in which the post-correction concentration increases as theabsolute temperature increases may be considered.

The inventors of the present application measured the concentrations ofCO₂, CO, NO, and C₃H₈ when the temperature of a measurement cell waschanged from 100° C. to 190° C. The calibration curve used at this timewas created using the measurement cell when the temperature thereof was180° C.

The changes in the concentration of each gas component at this time areshown in FIG. 3. It was found that, as is shown in FIG. 3, the CO₂concentration could not be corrected by means of a correction formulathat uses an equation of state for a gas that changes proportionally tothe absolute temperature. It was also found that the NO concentrationand the C₃H₈ concentration exhibited the same type of behavior dependingon the temperature range.

When the test samples have high concentrations, because the opticalabsorption spectrum becomes saturated (i.e., peaks out), it is thoughtthat the aforementioned behaviors may be due to the fact that theabsorption of a wavelength band or wavenumber band having a small degreeof absorbance located at the edge regions of the absorption band in theoptical absorption spectrum is used. More specifically, in simulationresults, in a central region of the absorption band in the opticalabsorption spectrum, the intensity decreases as the temperatureincreases according to conventional theory. However, in edge regions ata distance from the central regions, the results show that the intensityincreases as the temperature increases. It is thought that the reasonfor this phenomenon is that, as is shown in FIG. 4, the existenceprobabilities when several rotation states having different energylevels are present change depending on the temperature.

In this manner, it is a principal object of the present invention toflexibly deal with and correct concentration changes that are caused bychanges between the temperature when a correction calibration curve iscreated and the temperature when a test sample is measured, withouthaving to rely on corrections made using an equation of state for a gas.

Means for Solving the Problem

In other words, a spectrophotometer according to the present inventionis a spectrophotometer that measures concentrations of measurementtarget components contained in a test sample from an optical spectrumobtained by irradiating light onto the test sample, and is provided witha concentration calculation unit that calculates concentrations of themeasurement target components from the optical spectrum using acalibration curve, and a concentration correction unit that, using atemperature correction formula that corresponds to a wavelength regionor a wavenumber region in which concentrations of the measurement targetcomponents are being determined, corrects concentration changes in themeasurement target components that accompany temperature differencesbetween a temperature when the calibration curve is created and atemperature when the concentrations are measured.

Moreover, a spectrophotometry method according to the present inventionis a spectrophotometry method in which concentrations of measurementtarget components contained in a test sample are measured from anoptical spectrum obtained by irradiating light onto the test sample,comprising a concentration calculation step in which concentrations ofthe measurement target components are calculated from the opticalspectrum using a calibration curve, and a concentration correction stepin which concentration changes in the measurement target components thataccompany temperature differences between a temperature when thecalibration curve is created and a temperature when the concentrationsare measured are corrected using a temperature correction formula thatcorresponds to a wavelength region or a wavenumber region in whichconcentrations of the measurement target components are beingdetermined.

According to the above-described invention, because concentrations ofmeasurement target components are corrected using a temperaturecorrection formula that corrects an amount of change in a temperaturewhen a concentration is measured compared to a temperature when acalibration curve was created, concentrations of measurement targetcomponents can be corrected without the calibration curve having to becorrected. Moreover, by creating a temperature correction formula inadvance for each measurement target component, corrections can be madeso as to correspond to any increase or decrease behavior in theconcentration of the measurement target components that are generated byincreases or decreases in the absolute temperature. Furthermore, as aconsequence of this, correcting concentrations of measurement targetcomponents can be performed in real time.

In an optical spectrum there are wavelength regions or wavenumberregions where absorbance signals generated by a plurality of componentsare mutually superimposed, and there are also wavelength regions orwavenumber regions where peak intensity becomes saturated. In order toreduce the effects of these, and perform accurate measurements ofconcentrations, the concentration calculation unit is formed so as tocalculate concentrations of the measurement target components usingpredetermined wavelength regions or wavenumber regions in the opticalspectrum. At this time, in order to perform temperature correctionsaccurately, it is desirable that the concentration correction unit use atemperature correction formula that corresponds to the wavelength regionor wavenumber region in which the concentrations of the measurementtarget components are being determined.

The wavelength region or wavenumber region used when concentrations ofmeasurement target components are calculated by the concentrationcalculation unit vary depending on the type of the measurement targetcomponents and the measurement range of the measurement targetcomponents. Because of this, in order for temperature correction to beperformed accurately, it is desirable that the concentration correctionunit update the temperature correction formula in accordance with thetype of the measurement target components or the measurement range ofthe measurement target components.

It is also desirable that the concentration calculation unit calculateconcentrations of a plurality of measurement target components usingmultivariate analysis, and that the concentration correction unitcorrect the concentration of each measurement target component using thetemperature correction formula set for each one of the plurality ofmeasurement target components.

It is also desirable that, in order to favorably correct concentrationsof measurement target components that exhibit behavior that cannot becorrected by means of correction that employs an equation of state for agas, the temperature correction formula output progressively smallervalues as the temperature increases. At this time, the temperaturecorrection formula is used to correct changes in energy levels that arecaused by the temperature of the measurement target components.

When the test sample is a gas, changes in energy levels that are causedby the temperature of the measurement target components tend to occureasily, so that the effects obtained when the present invention isapplied are even more conspicuous.

As a specific embodiment for calculating the temperature correctionformula automatically, it is desirable that there be further provided astandard spectrum acquisition unit that acquires respective opticalspectra of a plurality of temperatures from standard test samples havingknown concentrations, and a correction formula creation unit thatcalculates the temperature correction formula from the standard spectraof the plurality of temperatures.

The wavelength region or wavenumber region used by the concentrationcalculation unit is updated depending on whether or not interferencecomponents are present, the type of measurement target components, andthe measurement range and the like. In order to make accuratecorrections corresponding to these updates, it is desirable that, whenthe wavelength region or wavenumber region used for the concentrationcalculation performed by the concentration calculation unit is updated,the correction formula creation unit update the temperature correctionformula so that it corresponds to the updated wavelength region orwavenumber region.

In a spectrophotometer, processing to update the calibration curve isperformed at regular intervals. In order to update the correctionformula so that it matches the update processing for the calibrationcurve, and thereby standardize the various processings, it is desirablethat the correction formula creation unit calculate the temperaturecorrection formula from the standard spectra obtained at the time thecalibration curve was created.

Effects of the Invention

According to the present invention which is formed in theabove-described manner, it is possible, even for components that aredifficult to correct simply by performing calculations using an equationof state for a gas, to correct temperature effects which differ for eachcomponent by flexibly dealing with concentration changes that are causedby changes between the temperature when a calibration curve was createdand the temperature when a test sample was measured, without having tocorrect the calibration curve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the structure of an infraredspectrophotometer according to the present embodiment.

FIG. 2 is a functional block diagram showing an information processingdevice of the same embodiment.

FIG. 3 depicts graphs showing relationships between the absolutetemperature and the concentration of each gas component.

FIG. 4 is a view showing changes in energy level that accompany changesin temperature.

BEST EMBODIMENTS FOR IMPLEMENTING THE INVENTION

Hereinafter, an embodiment of an infrared spectrophotometer according tothe present invention will be described with reference to the drawings.

An infrared spectrophotometer 100 according to the present embodiment isan exhaust gas analyzer that, for example, measures, as time seriesdata, concentrations of a plurality of components that are contained inexhaust gas, which is serving as a test sample, that is emitted from aninternal combustion engine of an automobile or the like.

More specifically, as is shown in FIG. 1, this infraredspectrophotometer 100 collects, for example, either a portion of or allof the exhaust gas emitted from a tailpipe of an automobile using a testsample collecting unit 2, and then, without diluting it, introduces theexhaust gas collected by the test sample collecting unit 2 into ameasurement cell 3, and then measures the respective concentrations of aplurality of components such as, for example, carbon monoxide (CO),carbon dioxide (CO₂), nitric oxide (NO), nitrogen dioxide (NO₂),nitrogen oxide (NO_(X)), and water (H₂O) and the like that are containedin the exhaust gas using an FTIR method. A temperature control mechanismH such as a heater or the like that controls the temperature of themeasurement cell 3 and of the gas inside the measurement cell 3 isprovided peripherally to the measurement cell 3. The temperature of themeasurement cell 3 is detected by a temperature sensor T1. Thistemperature control mechanism H is controlled by a computing device COMbased on temperatures detected by the temperature sensor T1 such that apredetermined temperature is obtained.

Moreover, in the infrared spectrophotometer 100, a suction pump 4 thatis used to introduce the exhaust gas into the measurement cell 3 isprovided on a downstream side of the measurement cell 3 on an exhaustgas line L1 on which the measurement cell 3 is provided. In addition tothese, valves 5 that adjust the flow rate of the exhaust gas, an orifice51, a flowmeter 6 that measures the flow rate of the exhaust gas, andfilters 7 that remove dust particles from the exhaust gas, and the likeare also provided on the exhaust gas line L1. Moreover, a calibrationgas supply line L2 that supplies the measurement cell 3 with zero gas orspan gas that is used to calibrate a photodetector 9, and a purge gasline L3 that is used to purify the exhaust gas line L1 or themeasurement cell 3 are also connected to the exhaust gas line L1 or themeasurement cell 3.

Furthermore, the infrared spectrophotometer 100 is also provided with alight irradiation unit 8 that irradiates interfered infrared light ontothe measurement cell 3, and the photodetector 9 that detects anintensity of the light that is emitted after being transmitted throughthe measurement cell 3. The computing device COM of the infraredspectrophotometer 100 calculates an optical absorption spectrum in theoptical spectrum of the exhaust gas using light intensity signalsobtained by the photodetector 9, and calculates the concentrations of aplurality of measurement target components from the absorbance of apredetermined wavelength region or wavenumber region in this opticalabsorption spectrum.

As is shown in FIG. 2, the computing device COM of the infraredspectrophotometer 100 is provided with a calibration curve storage unit10 that stores calibration curve data showing relationships betweenabsorbances of measurement target components and concentrations ofmeasurement target components, a concentration calculation unit 11 thatcalculates concentrations of measurement target components from opticalabsorption spectra and calibration curves shown by the calibration curvedata, and a concentration correction unit 12 that correctsconcentrations of measurement target components using temperaturecorrection formulas.

The calibration curve storage unit 10 stores calibration curve datacreated at a predetermined temperature (for example, at a referencetemperature). Relationships between the concentrations of each component(formed by a plurality of representative values, for example, in thecase of CO, concentrations of 2%, 4%, 6%, 8%, and the like) and therespective absorbances thereof are determined on this calibration curve.This calibration curve data can be created by a calibration curvecreation unit 16 (described below). Note that the calibration curve datamay be in the form of an arithmetical expression, or may be in tabularform.

The concentration calculation unit 11 acquires light intensity signalsfrom the photodetector 9, and also acquires calibration curve data fromthe calibration curve storage unit 10, and then calculates opticalabsorption spectra from the light intensity signals, and then usesmultivariate analysis to calculate the concentrations of eachmeasurement target component from the absorbance in a predeterminedwavelength region or wavenumber region of the relevant opticalabsorption spectrum, and from the calibration curve shown by thecalibration curve data.

The concentration correction unit 12 uses a temperature correctionformula set for each relevant measurement target component to performtemperature correction on the concentrations of each measurement targetcomponent obtained by the concentration calculation unit 11 based ontemperatures detected by the temperature sensor T1. The correctionformula data showing the temperature correction formula is stored in acorrection formula storage unit 17.

Here, temperature correction formulas are used to correct changes in theconcentrations of the measurement target components that accompanytemperature differences between the temperature of the measurement cell3 at the time when the calibration curve was created, and thetemperature of the measurement cell 3 at the time when the concentrationwas measured. Temperature correction formulas are determined inaccordance with the wavelength region or the wavenumber region in whichthe concentrations of the measurement target components are beingdetermined. The temperature correction formulas of the presentembodiment are determined from a polynomial in the form of atemperature-concentration relational formula (for example, the formulagiven below in Equation 2).

More specifically, the following formulas can be considered as examplesof temperature-concentration relational formulas. Namely, (1) a formulain which the concentration increases as the absolute temperatureincreases, (2) a formula in which the concentration decreases as theabsolute temperature increases, and (3) a formula in which, within apredetermined range, the concentration increases as the absolutetemperature increases, while once that predetermined range is exceeded,the concentration decreases as the absolute temperature increases.

For example, the temperature-concentration relational formula for CO₂ isa formula in which the concentration increases steadily as thetemperature increases. Moreover, the temperature-concentrationrelational formula for CO is a formula in which the concentrationdecreases steadily as the temperature increases. Furthermore, thetemperature-concentration relational formula for NO is a formula inwhich the concentration switches from a steady increase as thetemperature increases to a steady decrease. Note that because it may bethought that the change in concentration arising from the change intemperature in the case of CO₂ is caused by a change in the energy levelthat is generated by the change in temperature, the temperaturecorrection formula for CO₂ can be described as a formula to correct thechange in the energy level that is generated by the change intemperature.

In order to create this temperature correction formula, the computingdevice COM of the infrared spectrophotometer 100 is further providedwith a standard spectrum acquisition unit 13 that acquires opticalabsorbance spectra for each of a plurality of temperatures from standardtest samples having known concentrations, and a correction formulacreation unit 14 that creates temperature correction formulas from thestandard spectra of the plurality of temperatures.

The standard spectrum acquisition unit 13 acquires a plurality of setsof spectrum data that show the respective standard spectra of aplurality of temperatures of a standard test sample at the time when acalibration curve was created or the like, and stores these sets ofspectrum data in a standard spectra storage unit 15. Here, the standardspectrum data may be obtained as a result of the standard spectrumacquisition unit 13 acquiring light intensity signals from thephotodetector 9 and then calculating the standard spectrum data, or maybe obtained as a result of a separate functional block such as theconcentration calculation unit 11 acquiring the light intensity signalfrom the photodetector 9 at the time when the calibration curve wascreated, and then calculating the standard spectrum data, which is thenreceived by the standard spectrum acquisition unit 13.

The correction formula creation unit 14 creates correction formula datashowing temperature correction formulas that correspond to therespective wavelength region or wavenumber region used by theconcentration calculation unit 11 to calculate the concentrations of theplurality of measurement target components. Additionally, when thewavelength region or wavenumber region used in the calculations for therespective measurement target components by the concentrationcalculation unit 11 is updated, the correction formula creation unit 14creates updated correction formula data showing temperature correctionformulas that correspond to the relevant updated wavelength region orwavenumber region.

Next, processing to calculate a temperature correction formula which isperformed in conjunction with the creation of the calibration curve inthe infrared spectrophotometer 100 will be described.

A standard test sample (i.e., calibration gas) having a knownconcentration is introduced into the measurement cell 3 whosetemperature has been adjusted to a predetermined reference temperature(for example, 100° C.). In this state, infrared light is irradiated ontothe measurement cell 3 from the light irradiation unit 8, and light thathas been transmitted through the measurement cell 3 is detected by thephotodetector 9. The standard spectrum acquisition unit 13 or the likethen calculates a standard spectrum from a light intensity signal outputfrom the photodetector 9, and stores this in the standard spectrastorage unit 15. Here, the temperature of the measurement cell 3 intowhich the calibration gas has been introduced is then raised from thereference temperature by, for example, 10° C. each time, and thestandard spectrum data at each temperature is also acquired.

Next, the calibration curve creation unit 16 of the spectrophotometer100 decides the wavelength region or wavenumber region to be used whencalculating the concentration of each measurement target component fromthe standard spectrum data obtained at the reference temperature, andcreates calibration curve data showing a calibration curve using theabsorbance in the relevant wavelength region and wavenumber region.

Furthermore, the concentration calculation unit 11 then determines theconcentrations of the measurement target components at each temperaturein the relevant wavelength region and wavenumber region from thecalibration curve data and the standard spectrum data obtained at theother temperatures. In addition, the correction formula creation unit 14creates correction formula data showing a temperature correction formulafrom the concentrations the measurement target components at eachtemperature obtained from the standard spectrum data, and from the knownconcentrations of the measurement target components of the calibrationgas.

Hereinafter, the temperature correction formula used by theconcentration correction unit 12 will be described. The temperaturecorrection formula used by the concentration correction unit 12 can beshown by the following.

$\begin{matrix}{C_{comp} = \frac{C_{unk}}{{a_{3}T^{3}} + {a_{2}T^{2}} + {a_{1}T} + a_{0}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Here, C_(comp) is the post-correction concentration of the measurementtarget components, and C_(unk) is the pre-correction concentration ofthe measurement target components. The coefficients a₀˜a₃ are fittingparameters.

This formula (Equation 1) can be determined in the following manner.

If fitting is performed using graphs (these are the graphs shown in FIG.3 in which the horizontal axis shows temperature while the vertical axisshows concentration) of the concentrations of measurement targetcomponents at each temperature obtained using a calibration gas having aknown concentration, then the following relational expression (i.e., atemperature—concentration relational expression) is obtained. Note thatin the following a third-order equation is used, however, it is alsopossible for a fourth-order equation or greater, or a first-order orsecond-order equation to be used.

$\begin{matrix}{\frac{C_{{bottle}\;\_\;{meas}}}{C_{bottle}} = {{a_{3}T^{3}} + {a_{2}T^{2}} + {a_{1}T} + a_{0}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Here, C_(bottle) is the known concentration of the measurement targetcompounds in the calibration gas. Moreover, C_(bottle) _(_) _(meas) isthe measurement value of the measurement target components in thecalibration gas at each temperature. The coefficients a₀˜a₃ are fittingparameters.

Because this relational expression is also valid when measuringmeasurement target components having unknown concentrations, therelationship between the post-correction concentration C_(comp), and thepre-correction concentration G_(unk) is as follows.

$\begin{matrix}{\frac{C_{unk}}{C_{comp}} = {{a_{3}T^{3}} + {a_{2}T^{2}} + {a_{1}T} + a_{0}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

The above-described formula (Equation 1) can be obtained by transformingthis relational expression (i.e., a temperature—concentration relationalexpression).

The correction formula creation unit 14 creates correction formula databy calculating the coefficients a₀˜a₃ for each one of the plurality ofmeasurement target components contained in the exhaust gas. Thecorrection formula data showing the coefficients a₀˜a₃ obtained by thecorrection formula creation unit 14 is then stored in the correctionformula storage unit 17.

According to the infrared spectrophotometer 100 of the presentembodiment which is formed in this manner, because the concentrations ofmeasurement target components are corrected using a temperaturecorrection formula that corrects an amount of change between thetemperature at the time when a calibration curve was created and thetemperature at the time when a concentration was measured, it ispossible to correct the concentrations of measurement target componentswithout having to correct the calibration curve. Additionally, bycreating a temperature correction formula for each measurement targetcomponent, corrections can be made so as to correspond to any increaseor decrease behavior in the concentrations of the measurement targetcomponents that are generated by increases or decreases in the absolutetemperature. Furthermore, as a consequence of this, correctingconcentrations of measurement target components can be performed in realtime.

Note that the present invention is not limited to the above-describedembodiment.

For example, in addition to a structure in which a temperaturecorrection formula is determined from standard spectrum data obtainedwhen a calibration curve is created, it is also possible to determine atemperature correction formula from standard spectrum data obtainedindependently of the calibration curve creation. In this case, it isnecessary for the temperature of the measurement cell 3 when thestandard spectrum data is acquired to be the same as the temperaturewhen the calibration curve is created.

Moreover, in the above-described embodiment, it is also possible for theconcentration correction unit 12 to determine whether or not to performa temperature correction in accordance with the wavelength region or thewavenumber region in which the concentration of the measurement targetcomponents is being determined. For example, it is also possible tocorrect concentrations using a temperature correction formula not whenthe wavelength region or wavenumber region is a central region of theabsorption band, but only when the wavelength region or wavenumberregion is a rise region of an edge region.

Furthermore, it is also possible for the concentration correction unit12 to correct a concentration using a temperature correction formulaonly when the concentration of a measurement target component is equalto or greater than a predetermined value.

In the above-described embodiment, it is also possible for theconcentration correction unit 12 to update the temperature correctionformula in accordance with the measurement range of the measurementtarget components.

Furthermore, in the above-described embodiment, a structure is employedin which the post-correction concentration is calculated after themeasurement values obtained by the concentration calculation unit 11have only been corrected once, however, it is also possible to employ astructure in which the same type of correction as that performed in theabove-described embodiment is additionally performed on concentrationsthat have already been corrected using a correction formula that uses anequation of state for a gas.

In the above-described embodiment, an analyzer that uses an FTIR methodis described, however, an analyzer that uses an NDIR method may also beused.

In the above-described embodiment, an example is described in whichtemperature correction is performed using the temperature T1 of themeasurement cell 3, however, it is also possible to perform thetemperature correction using the temperature of the gas inside themeasurement cell 3.

Moreover, the spectrophotometer of the present invention is not limitedto using infrared light, and a spectrophotometer that uses ultravioletlight or one that uses visible light may also be used.

Moreover, in the above-described embodiment, a case in which the presentinvention is applied to an exhaust gas analyzer that analyzes exhaustgas emitted from an internal combustion engine is described, however,the present invention may also be applied to an exhaust gas analyzerthat analyzes exhaust gas emitted from a factory or a power plant, or toan exhaust gas analyzer that analyzes other types of test sample gas.Furthermore, the test sample is not limited to being a gas, and may be aliquid such as a liquid chemical or the like.

Furthermore, it should be understood that the present invention is notlimited to the above-described embodiment, and that variousmodifications and the like may be made thereto insofar as they do notdepart from the spirit or scope of the present invention.

DESCRIPTION OF THE REFERENCE NUMERALS

-   100 . . . Infrared spectrophotometer-   11 . . . Concentration Calculation Unit-   12 . . . Concentration Correction Unit-   13 . . . Standard Spectrum Acquisition Unit-   14 . . . Correction Formula Creation Unit

What is claimed is:
 1. A spectrophotometer that measures concentrationsof measurement target components contained in a test sample from anoptical spectrum obtained by irradiating light onto the test sample,comprising: a concentration calculation unit that calculatesconcentrations of the measurement target components from the opticalspectrum using a calibration curve; and a concentration correction unitthat, using a temperature correction formula that corresponds to awavelength region or a wavenumber region in which concentrations of themeasurement target components are being determined, correctsconcentration changes in the measurement target components thataccompany temperature differences between a temperature when thecalibration curve is created and a temperature when the concentrationsare measured.
 2. The spectrophotometer according to claim 1, wherein theconcentration correction unit updates the temperature correction formulain accordance with the type of the measurement target components or themeasurement range of the measurement target components.
 3. Thespectrophotometer according to claim 1, wherein the concentrationcalculation unit calculates concentrations of a plurality of measurementtarget components using multivariate analysis, and the concentrationcorrection unit corrects the concentration of each measurement targetcomponent using the temperature correction formula set for each one ofthe plurality of measurement target components.
 4. The spectrophotometeraccording to claim 1, wherein the temperature correction formula is aformula that outputs progressively smaller values as the temperatureincreases.
 5. The spectrophotometer according to claim 1, wherein thetest sample is a gas, and the temperature correction formula is used tocorrect changes in energy levels that are caused by the temperature ofthe measurement target components.
 6. The spectrophotometer according toclaim 1, wherein the concentration correction unit correctsconcentrations of the measurement target components using thetemperature correction formula only when the wavelength region orwavenumber region in which the concentration of the measurement targetcomponents is being determined is a different region from a centralregion of the absorption band.
 7. The spectrophotometer according toclaim 1, further comprising: a standard spectrum acquisition unit thatacquires respective optical spectra of a plurality of temperatures fromstandard test samples having known concentrations; and a correctionformula creation unit that creates the temperature correction formulafrom the standard spectra of the plurality of temperatures.
 8. Thespectrophotometer according to claim 7, wherein, when the wavelengthregion or wavenumber region used for the concentration calculationperformed by the concentration calculation unit is updated, thecorrection formula creation unit updates the temperature correctionformula so as to correspond to the relevant updated wavelength region orwavenumber region.
 9. The spectrophotometer according to claim 7,wherein the correction formula creation unit calculates the temperaturecorrection formula from the standard spectra obtained at the time thecalibration curve was created.
 10. A spectrophotometer that measuresconcentrations of measurement target components contained in a testsample from an optical spectrum obtained by irradiating light onto thetest sample, comprising: a concentration calculation unit thatcalculates concentrations of the measurement target components from theoptical spectrum using a calibration curve; and a concentrationcorrection unit that, using a predetermined temperature correctionformula, corrects concentration changes in the measurement targetcomponents that accompany temperature differences between a temperaturewhen the calibration curve is created and a temperature when theconcentrations are measured.
 11. A spectrophotometry method in whichconcentrations of measurement target components contained in a testsample are measured from an optical spectrum obtained by irradiatinglight onto the test sample, comprising: a concentration calculation stepin which concentrations of the measurement target components arecalculated from the optical spectrum using a calibration curve; and aconcentration correction step in which concentration changes in themeasurement target components that accompany temperature differencesbetween a temperature when the calibration curve is created and atemperature when the concentrations are measured are corrected using atemperature correction formula that corresponds to a wavelength regionor a wavenumber region in which concentrations of the measurement targetcomponents are being determined.
 12. A non-transitory computer-readablerecording medium storing a spectroscopic analysis program that is usedin a spectrophotometer that measures concentrations of measurementtarget components contained in a test sample from an optical spectrumobtained by irradiating light onto the test sample, and that provides acomputer with: a function of a concentration calculation unit thatcalculates concentrations of the measurement target components from theoptical spectrum using a calibration curve; and a function of aconcentration correction unit that, using a temperature correctionformula that corresponds to a wavelength region or a wavenumber regionin which concentrations of the measurement target components are beingdetermined, corrects concentration changes in the measurement targetcomponents that accompany temperature differences between a temperaturewhen the calibration curve is created and a temperature when theconcentrations are measured.